Silicon wafers are generally processed or polished using a CMP apparatus, which includes a lower board having a circular rotational plate equipped with a polishing pad, an upper board to closely adhere a silicon wafer to the polishing pad, and a device to feed slurry on the polishing pad.
A CMP process includes pushing a semiconductor wafer, on which an integrated circuit is formed, in an opposite direction to a driven polishing pad such that oxides including Si based deposits are removed from the wafer, and producing a planar surface with high smoothness on the wafer. During the CMP process, the wafer and an interface of the polishing pad is coated with deionized water and/or a chemically active reagent as well as a polishing solution.
Recently, a magnetic recording medium such as a magnetic disk is demanded to increase capacity and/or memory density according to advanced technology innovations and, therefore, there is a requirement for development of high density integration of substrates during surface processing.
According to increased capacity and/or memory density, a gap between a recording disk and a magnetic head, that is, a fly height of the magnetic head is reduced. Due to considerably decreased fly height, if a protrusion formed on a surface of a magnetic recording disk, the protrusion may contact a magnetic head to cause head crash, resulting in damage to the surface of the magnetic disk. Also, even with a microfine protrusion substantially not causing the head crash, it may contact the magnetic head and possibly cause malfunction in reading and writing information. Additionally, because of the protrusion, the magnetic head may be in close contact with the surface of the disk, causing a problem of not allowing the magnetic head to fly properly.
In order to prevent such a close contact between the recording disk and the magnetic head, surface treatment such as a texturing process is generally carried out to give microfine streaks on the surface of a substrate used in a recording disk. Such a texturing process controls orientation of crystal growth when a metal magnetic layer is formed on the substrate of the recording disk, so that the recording disk has increased coercive force in a recording direction thereon, which in turn, results in improved recording density of the recording disk.
As an example of the texturing process, a slurry polishing method using a polishing pad applied with a slurry of glass grinding stone particles has been used.
For instance, a method for manufacturing a magnetic recording substrate of a hard disk often used as a magnetic recording medium generally comprises a smoothing processing or planarization (hereinafter referred to as “planarization”) to prepare a planar surface of aluminum, glass, etc., treating the planar surface by non-magnetic plating such as a nickel phosphorous coating, forming a magnetic thin layer made of cobalt based alloys, and coating the magnetic thin layer with a surface protective layer made of carbon materials to produce the substrate.
In recent years, there is an increased requirement for polishing pads used in planarization of a magnetic recording substrate. Especially, the final step of the planarization often includes surface treatment called a “texturing process”, which uses slurry containing abrasive particles dispersed therein and a polishing pad so as to form microfine trenches on a surface of a recording disk. Accordingly, there remains a need for development of an optimal polishing pad to embody high capacity and/or memory density magnetic disks.
Conventional CMP processes using polishing pads have been disclosed, in particular, Japanese Patent Laid-Open No. 2005-329491 disclosed a polishing pad with structure of a pad A and an elastomeric polymer coating layer B placed on the pad A, wherein the pad A comprises a non-woven fabric consisting of nylon staple fibers with 1 to 5 denier and is prepared by impregnating the fabric with the same elastomeric polymer as used in the coating layer B, especially, polyurethane resin, as shown in FIG. 4.
However, this polishing pad was manufactured by preparing the pad A through impregnation of the non-woven fabric with polyurethane resin and, then, applying the same polyurethane resin to the pad A to form a coating layer. For this reason, the polishing pad described above needs composite processes and encounters a problem that it is difficult to uniformly control a size of pores in the coating layer B.
Furthermore, when the coating layer B is completely worn out, the polishing pad cannot be used any more even though the pad A under the coating layer B remains unchanged or unworn. Therefore, this has problems of short product life and/or causing a great amount of waste of raw materials.
Japanese Patent Laid-Open No. H9-59395 proposed a polishing pad which comprises a non-woven fabric consisting of synthetic staple fibers with 1 to 5 denier and is prepared by impregnating the fabric with polyurethane resin. However, since the synthetic staple fiber has high monofilament fineness and, thus, high modulus, the staple fibers arranged on a surface of the polishing pad have an increased orientation angle of 30 to 50°, which is an angle of the fiber to the polishing pad in a longitudinal direction thereof.
Such a polishing pad described above exhibits an irregular surface and has thick staple fibers arranged on the surface of the pad, thereby causing a lack of pores between the fibers and a decrease in polishing performance of the pad.
Further, Japanese Patent Laid-Open Nos. 2005-074609 and 2001-67659 disclosed a polishing pad for a magnetic recording medium which comprises (i) a non-woven fabric made of ultrafine fibers and (ii) elastomeric polymer impregnated into the non-woven fabric, and in which the ultrafine fibers are arranged and raised on a surface of the polishing pad.
However, the ultrafine fibers arranged on the surface of the polishing pad are too much parallel in the longitudinal direction of the pad, that is, have a very small orientation angle θ2, as well as a fiber raising angle θ1 of the ultrafine fibers raised on the surface thereof so small that a binding force between bundles of ultrafine fibers is excessively high to deter slurry particles from smoothly flowing during the texturing process, resulting in agglomeration of the particles. Therefore, the polishing pad disclosed in the above patent has disadvantages of reduced polishing performance and many scratches occurring on a polished surface of a magnetic recording medium.